Reflectometer, spectrophotometer, ellipsometer or polarimeter system including sample imaging system that simultaneously meets scheimpflug condition and overcomes keystone error

ABSTRACT

An imaging system, and method of its use, for viewing a sample surface at an inclined angle, preferably in functional combination with a sample investigating reflectometer, spectrophotometer, ellipsometer or polarimeter system; wherein the imaging system provides that a sample surface and multi-element imaging detector surface are oriented with respect to one another to meet the Scheimpflug condition, and wherein a telecentric lens system is simultaneously positioned between the sample surface and the input surface of the multi-element imaging detector such that an image of the sample surface produced by said multi-element imaging detector is both substantially in focus over the extent thereof, and such that substantially no keystone error is demonstrated in said image.

This Application is a CIP of application Ser. No. 14/815,625 Filed Mar.13, 2013, and therevia Claims Benefit of 61/849,178 Filed Jan. 22, 2013.

TECHNICAL FIELD

The present invention relates to reflectometers, spectrophotometers,ellipsometers and polarimeters, and more particularly to areflectometer, spectrophotometer, ellipsometer or polarimeter systemwherein an investigated sample surface is obliquely moniored by animaging detector, a surface of which is oriented with respect to asample surface so as to meet the Scheimpflug condition, and wherein atelecentric lens system, or a functionally afocal equivalent, issimultaneously positioned between said sample surface and the inputsurface of said imaging detector, such that an image of said samplesurface produced by said imaging detector is both substantially in focusover an extent thereof, and such that substantially no keystone error isdemonstrated in said image.

BACKGROUND

It is known to investigate monitored surfaces of samples using beams ofelectromagnetic radiation, as in reflectometry, ellipsometry,polarimetry and spectrophotometry. However, a problem exists whenoblique angle monitoring of a sample surface is desirable. The problemis that it is difficult to maintain a focused image over an extent ofsaid surface, and simultaneously compensate for Keystone error in saidimage.

It is known to orient sample surfaces and detector input surfaces sothat the Scheimpflug condition is met to attain focus of a samplesurface at said detector over an extent of said sample surface, (seePatent to Liphardt et al. U.S. Pat. No. 8,953,030 for instance, whichconcerns data aquisition, and which Issued after the Effective PriorityDate of this Application). And it is known to apply Telecentric lenssystems to compensate for Keystone error, (see Patent to Giles et al.U.S. Pat. No. 5,548,394 which teaches a fingerprint scanner that appliesmeeting the Scheimpflug condition and applies a Telecentric Lens toarrive at a system that provides the ability to scan a fingerprint andprovide a true image thereof, in focus, and without varyingmagnification, Keystone varying effects). However, in the context ofreflectometers, spectrophotometers, ellipsometers and polarimeters it isbelieved new, novel and non-obvious to simultaneously both meet theScheimpflug condition by properly orienting sample and Imaging detectorinput surfaces with respect to one another, and to simultaneously applya telecentric lens, or functionally equivalent afocal system, betweensaid sample surface and detector surface to compensate Keystone error.

As a prosecution history exists with respect to application Ser. No.13/815,625, which Application is under Appeal regarding Claimssubstantially equivalent claims 1-12 herein, it is mentioned that theGiles 394 Patent, teaches a fingerprint scanner that applies Scheimpflugand the Telecentric Lens conditions to arrive at a system that providesthe ability to scan a fingerprint and provide a true image thereof, infocus, and without varying magnification, Keystone varying effects.While Applicant considers this prior art relevant, it was not used infashioning a rejection by the Examiner in the 625 Application. It isalso noted that this reference does not hint at, let alone describe soas to obviate application in an ellipsometer etc. system, nor does itteach providing contrast enhancing polarizer and/or compensator in thepath between a sample being imaged and an imaging detector.Additionally, nothing in said Giles et al. 394 Patent remotely suggestsremoval of the Prism (10) therein, (or other elements present thereinbut not in the present invention, eg. the scanning mirrors etc. in Gileset al. 394), which Prism (10) is applied in Giles et al. 394 to supporta finger from which a finger print is being imaged in use, andreplacement thereof with a stage in an ellipsometer etc. system, whichstage supports a sample during an investigation thereof. There isabsolutely nothing in Giles et al. 394 that would guide one skilled inthe art and acting as a technician rather than an inventor, to removesaid Prism (10) therein as the invention therein would not thenfunction! And again, the Giles et al. 394 Patent does not remotelyobviate placing a polarizer and/or compensator, as shown in the Original625 Parent Application in FIG. 4, between a finger on a prism andimaging detector, nor does Giles et al. 394 provide any teachings as howto pick and choose elements disclosed therein, while rejecting others,and then modify and combine said selected elements to arrive at thepresent invention. One skilled in the art having Giles et al. 394 beforehim or her, (and other known references), would not remotely arrive atthe present invention. He or she would not even find any hint that suchshould be done. To the extent that application of the ScheimpflugCondition and Telecentric Lensing is known from a reading of Giles etal. 394, there still remains no suggestion that such should be appliedin a reflectometer, spectrophotometer, ellipsometer or polarimetersystem. The Examiner in the Parent 625 Application cited a caseidentified as In re Keller 642F2d 413, 208 USPQ 871 (CCPA 1981) andapplied a standard to the effect that if a prior art structure iscapable of carrying out an intended function then it meets the Claim.Applied properly, if the prior art presents such structure as In reKeller requires, this is true. However, Attorney Welch expresses hisopinion that the Examiner MUST Allow Claims to a new, novel, non-obviousand useful invention.

Continuing, a computer search for Patents that including the Terms“Scheimpflug and Reflectometer” has identified U.S. Pat. Nos. 7,872,751and 7,567,345. And a similar computer search for Patents containing theterms “Telecentric and Reflectometer provided U.S. Pat. Nos. 8,160,351,7,898,661, 7,859,659, 7,777,878, 7,719,677, 7,656,519, 7,477,372,7,460,248, 7,190,460, 7,084,967, 7,075,637, 6,888,627, 6,862,090,6,832,843, 6,636,302, 6,437,312, 6,370,422, 5,094,523 and 4,660,984. Nooverlap in said two searches is identified.

A search for Patents that including the Terms “Scheimpflug andSpectrophotometer” has identified U.S. Pat. Nos. 7,872,751, RE41,906,7,653,428, RE40,225, 7,107,092, RE38,153, 5,874,455, 5,764,365,5,665,770, 5,517,312 and 4,895,445. And, a search for Patent containingthe terms “Telecentric and Spectrophotometer provided U.S. Pat. Nos.8,218,152, 8,194,283, 8,189,170, 8,149,381, 8,008,642, 7,993,613,7,957,067, 7,898,912, 7,897,912, 7,859,659, 7,800,014, 7,777,878,7,723,662, 7,698,068, 7,697,111, 7,652,792, 7,583,386, 7,428,056,7,408,649, 7,352,459, 7,336,354, 7,166,163, 7,113,281, 7,086,863,6,922,236, 6,895,158, 6,850,371, 6,835,683, 6,832,824, 6,765,724,6,672,109, 6,649,268, 6,687,262, 6,153,873, 6,108,083, 6,008,905,5,812,419, 5,680,209 and 3,972,627. Again, there is no overlap in theidentified searches.

A computer search for Patents including the Terms “Polarimeter andTelecentric” has identified U.S. Pat. Nos. 8,160,351, 7,777,878,7,221,420, 7,079,247, 7,061,561, 7,038,776 and 6,927,888. A computersearch for Patents including the Terms “Polarimeter and Scheimpflug” hasidentified U.S. Pat. Nos. 7,872,751 and 7,567,345. It is noted thatthere is no overlap in the two identified searches.

Similarly a computer search for Patents including the Terms“Ellipsometer and Telecentric” has identified U.S. Pat. Nos. 8,175,831,8,111,376, 8,054,467, 7,898,661, 7,864,296, 7,859,659, 7,791,732,7,777,878, 7,719,677, 7,636,168, 7,583,386, 7,428,056, 7,408,649,RE39,978, 7,221,420, 7,190,460, 7,151,609, 7,061,561, 6,879,3806,862,090, 6,737,207, 6,592,574, 6,583,877, 6,525,806, 6,507,441,6,493,097, 6,323,946, 6,177,990, 6,008,892, 5,917,594 and 5,646,733.Whereas a search for the Patents including the Terms “Ellipsometer andScheimpflug” provided U.S. Pat. No. 7,872,751, RE41,906, 7,724,362,7,567,345, RE40,225, 6,592,574, RE38,153, 5,963,326, 5,764,365 and5,517,312. Again, but for the U.S. Pat. No. 6,592,574, no overlap isidentified in the two searches except for the U.S. Pat. No. 6,592,574,and this Patent does not suggest a combined Scheimpflug and telecentricsystem, but rather suggests using said systems separately in differentembodiments of a system for laser sculpting of eye tissue.

In addition, Patents to Liphardt et al., U.S. Pat. Nos. 7,567,345,7,872,751 and 8,013,966 are identified as they discuss the Scheimpflugcondition referenced to a detector in a system that uses electromagneticradiation to investigate a sample, that describe additional alignment orimaging systems above a sample in addition to sample investigatingelements and that describe a spatial filter. Another Patent to Liphardt,U.S. Pat. No. 8,345,241 is identified as it mentions both theScheimpflug condition, and Telecentric imaging in an ellipsometer systemthat includes a digital light processor. A Patent to Horie, U.S. Pat.No. 7,095,498 describes the presence of a pinhole mirror in aspectroscopic ellipsometer system. The pinhole mirror is rotated so thata beam of electromagnetic radiation is oriented along a locus which isoblique angle, rather than along a normal thereto. A Patent to Masao,U.S. Pat. No. 5,963,326 describes an imaging ellipsometer which uses alarge cross-section measuring beam rather than a small beam spot as isthe focus in the present invention. A Patent to Finarov, U.S. Pat. No.5,517,312 mentions the Scheimpflug condition in the context of ascanning ellipsometer wherein a beam is scanned over a sample and apattern recognition camera which is designed to utilize the Scheimpflugcondition, is applied. Other known Patents are U.S. Pat. No. 751,347 toScheimpflug, U.S. Pat. No. 2,380,210 to Bennett, U.S. Pat. No. 3,565,511to Dilworth, U.S. Pat. No. 3,773,404 to Moore, U.S. Pat. No. 6,271,972to Kedar et al., U.S. Pat. No. 6,246,067 to Tullis, and U.S. Pat. No.5,625,495 to Moskovich. These Patents describe various aspects of theScheimpflug Condition and Telecentric Lensing in other than the contextof Ellipsometer etc. systems.

It is also noted that in prosecution of the parent application Ser. No.13/815,625, the Examiner cited U.S. Pat. No. 7,084,978 to Liphardt, U.S.Pat. No. 5,706,083 to Lida et al. and Published Application 2002/0039184by Sandusky. In that prosecution Applicant strongly argued that theExaminer had completely missed the focus of the present invention.Liphardt 978 Patent does not concern oblique Angle Imaging, and Lida 083does not apply any telecentric lens in it's oblique angle Imagingsystem, (ie. Lida element Nos. 30 (lamp) and 31 (CCD Camera)), nor doesit, or Liphardt 978, mention the Scheimpflug condition for achievingfocusing in an imaging system over an area of a sample at an obliqueangle in the area of ellipsometers and related systems.

Finally, two papers titled “Telecentric Lens” and “ScheimpflugPrinciple” are identified and included in the Information Disclosurewhich fairly concisely describe the indicated topics and were downloadedfrom Wikipedia.

In view of the foregoing, a need for a system selected from the group ofreflectometer, ellipsometer, polarimeter and spectrophotometer, istherefore identified, which system simultaneously provides benefitsinherent in meeting the Scheimpflug condition between a sample surfaceand a detector surface, simultaneous with applying a telecentric lenssystem or functionally equivalent afocal system, is identified.

DISCLOSURE OF THE INVENTION

The present invention is an oblique angle imaging system, comprising:

a) a source of illuminating electromagnetic radiation;

b) a stage for supporting a sample placed thereupon;

said oblique angle imaging system source of illuminating electromagneticradiation being oriented with respect to said stage for supporting asample such that in use an illuminating beam of electromagneticradiation is directed from said source toward said stage at an obliqueangle to said stage;

c) a telecentric lens system sequentially comprising:

-   -   at least one lens;    -   an aperture having a diameter; and    -   at least one lens.        Said telecentric lens system is characterized in that at least        one selection from the group consisting of:    -   the entry pupil is substantially at infinity, where “pupil”        refers to a selection from the group consisting of:        -   object of an aperture; and        -   image of an aperture;            and    -   the exit pupil is substantially at infinity, where “pupil”        refers to a selection from the group consisting of:        -   object of an aperture; and        -   image of an aperture.            The system further comprises:

d) a multi-element imaging detector having an input surface.

Said stage and multi-element imaging detector are oriented with respectto one another with the surface of said sample placed on said stage andthe input surface of said multi-element imaging detector meeting theScheimpflug condition, and in conjunction with said telecentric lenssystem, which is simultaneously positioned between said sample surfaceand the input surface of said multi-element imaging detector results inan image of said sample surface produced by said multi-element imagingdetector which is both substantially in focus, and demonstratessubstantially no keystone error in said image.Said oblique angle imaging system is characterized by the limitingcombination of said sample surface and multi-element imaging detectorsurface being oriented to meet the Scheimpflug condition to effect focusof said sample, in combination with said telecentric lens between saidsample surface and said imaging detector surface to substantiallyovercome keystone error.

The present invention is more specifically a reflectometer,spectrophotometer, ellipsometer or polarimeter system comprising anoblique angle imaging system for viewing a sample.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem comprises:

-   -   a source of a sample investigating beam of electromagnetic        radiation;    -   a stage for supporting a sample placed thereupon; and    -   a detector.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem source, stage and detector are, in use, oriented so that saidsource directs a sample investigating beam of electromagnetic radiationto a sample placed on said stage so that it impinges on a spot thereof,interacts therewith and enters said detector.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem can further comprise at least one selection from the groupconsisting of:

-   -   a polarizer/analyzer; and    -   a compensator;        between the sample and the imaging detector to enable effecting        a polarization state in said sample imaging beam of        electromagnetic radiation.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem can further comprise at least one selection from the groupconsisting of:

-   -   a polarizer/analyzer; and    -   a compensator;        between said source of a sample investigating beam of        electromagnetic radiation and said detector thereof, to enable        effecting a polarization state in said sample investigating beam        of electromagnetic radiation.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem can provide that the source of illuminating electromagneticradiation and the source of sample investigating electromagneticradiation can be derived from a common source of electromagneticradiation.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem for viewing a sample can provide that said aperture diameter isadjustable.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem for viewing a sample can provide that the oblique angle of saidilluminating electromagnetic radiation is at, or near the Brewster anglefor the sample being investigated.

A method of imaging and investigating a sample with electromagneticradiation comprises the steps of:

a) providing a reflectometer, spectrophotometer, ellipsometer orpolarimeter system also comprising an oblique angle imaging system forviewing a sample;

-   -   said reflectometer, spectrophotometer, ellipsometer or        polarimeter system comprising:        -   a source of a sample investigating beam of electromagnetic            radiation;        -   a stage for supporting a sample placed thereupon; and        -   a detector.

Said reflectometer, spectrophotometer, ellipsometer or polarimetersystem source, stage and detector are oriented so that said sourcedirects a sample investigating beam of electromagnetic radiation to asample placed on said stage so that it impinges on a spot thereof,interacts therewith and enters said detector.

Further, said oblique angle imaging system, comprises:

a′) a source of illuminating electromagnetic radiation;

b′) said stage for supporting a sample placed thereupon;

said oblique angle imaging system source of illuminating electromagneticradiation being oriented with respect to said stage for supporting asample such that in use an illuminating beam of electromagneticradiation is directed from said source toward said stage at an obliqueangle to said stage.

The present invention system further comprises:

c′) a telecentric lens system sequentially comprising:

-   -   at least one lens;    -   an aperture having a diameter; and    -   at least one lens;        said telecentric lens system being characterized in that at        least one selection from the group consisting of:    -   the entry pupil is substantially at infinity, where “pupil”        refers to a selection from the group consisting of:        -   object of an aperture; and        -   image of an aperture;            and    -   the exit pupil is substantially at infinity, where “pupil”        refers to a selection from the group consisting of:        -   object of an aperture; and        -   image of an aperture.

And said system further comprises:

d′ a multi-element imaging detector having an input surface.

Said stage and multi-element imaging detector are oriented with respectto one another with the surface of said sample placed on said stage andthe input surface of said multi-element imaging detector meeting theScheimpflug condition, and in conjunction with said telecentric lenssystem, which is simultaneously positioned between said sample surfaceand the input surface of said multi-element imaging detector results inan image of said sample surface produced by said multi-element imagingdetector which is both substantially in focus, and demonstratessubstantially no keystone error in said image.

Further, said source of illuminating electromagnetic radiation providesilluminating electromagnetic radiation to a spot on said sample uponsaid stage which is coincident with the location on said sample whereatsaid sample investigating beam of electromagnetic radiation impinges.

The oblique angle imaging system is characterized by the limitingcombination of said sample surface and multi-element imaging detectorsurface being oriented to meet the Scheimpflug condition to effect focusof said sample, in combination with said telecentric lens between saidsample surface and said imaging detector surface to substantiallyovercome keystone error.

Said method further comprises:

b) orienting said sample surface and multi-element imaging detectorsurface to meet the Scheimpflug condition and positioning saidtelecentric lens system between said sample surface and multi-elementimaging detector surface so that, in an image of said sample surfacewhen produced by said multi-element imaging detector, demonstratessubstantially no keystone error and said image is substantially in focusover its entire extent;

c) causing said source of illuminating electromagnetic radiation todirect illuminating electromagnetic radiation to reflect from saidsample surface, pass through said telecentric lens system and enter saidmulti-element imaging detector;

d) causing said multi-element imaging detector to produce an image ofsaid sample surface that is substantially free of keystone error and issubstantially in focus.

Said method can further comprise providing a computer and at least oneselection from the group consisting of:

-   -   steps c) and d) are carried out under control thereof; and    -   the method includes storing at least some output provided by the        multi-element imaging detector in a non-transitory machine        readable media, and analyzing at least some output provided        thereby;        applies.

Said method can further comprise that said computer receives data fromsaid multi-element imaging detector and corrects it for image aspectratio prior to display.

Said method can further provide that the system further comprises atleast one selection from the group consisting of:

-   -   a polarizer/analyzer; and    -   a compensator;        between the sample and the imaging detector to enable effecting        a polarization state in said sample imaging beam of        electromagnetic radiation.

Said method can further provide that the system further comprises atleast one selection from the group consisting of:

-   -   a polarizer/analyzer; and    -   a compensator;        between said source of a sample investigating beam of        electromagnetic radiation and said detector thereof, to enable        effecting a polarization state in said sample investigating beam        of electromagnetic radiation.

As presented in the Parent 625 Application and included here forbrevity, the present invention is an imaging system for viewing a sampleat an inclined angle comprising:

a) a source of illuminating electromagnetic radiation;

b) an optional collimator;

c) a stage for supporting a sample placed thereupon;

d) a telecentric lens system; and

e) a multi-element imaging detector having an input surface.

The system is distinguished in that said stage and multi-element imagingdetector are oriented with respect to one another such that the surfaceof said sample placed on said stage and the input surface of saiddetector meet the Scheimpflug condition, and said telecentric lenssystem is simultaneously positioned between said sample surface and theinput surface of said multi-element imaging detector such that an imageof said sample surface produced by said detector is both substantiallyin focus, and such that substantially no keystone error is demonstratedin said image.

Said imaging system for viewing a sample at an inclined angle an furthercomprises a computer for receiving data from said multi-element imagingdetector and correcting it for image aspect ratio.

Said imaging system for viewing a sample at an inclined angle canfurther comprise at least one polarizer between said source ofilluminating electromagnetic radiation and said multi-element imagingdetector to enable effecting a polarization state in a beam ofelectromagnetic radiation produced by said source thereof, and can alsofurther comprise at least one compensator between said source ofilluminating electromagnetic radiation and said detector to furtherenable effecting a polarization state in a beam of electromagneticradiation produced by said source thereof.

Said imaging system for viewing a sample at an inclined angle providesthat said telecentric lens system can comprise, in sequence:

-   -   at least one lens;    -   an aperture having a diameter; and    -   at least one lens;        and said aperture diameter can be adjustable.

As a result of the present invention system configuration making spaceavailable, said system for viewing a sample at an inclined angle canfurther comprises a second imaging, or metrology system positionedsubstantially above said sample surface and between said source of abeam of electromagnetic radiation and said multi-element imagingdetector having an input surface.

During use, illuminating electromagnetic radiation provided by thatsource thereof can approaches the sample surface along an oblique angle,which can be at, or near the Brewster angle for the sample beinginvestigated.

A modified description provides that an imaging system for viewing asample at an inclined angle, is in functional combination with areflectometer, spectrophotometer, ellipsometer or polarimeter system.

In said modified imaging system for viewing a sample at an inclinedangle, the imaging system comprises:

a) a source of illuminating electromagnetic radiation;

b) an optional collimator;

c) a stage for supporting a sample placed thereupon;

d) a telecentric lens system; and

e) a multi-element imaging detector having an input surface.

As before, said stage and multi-element imaging detector are orientedwith respect to one another such that the surface of said sample placedon said stage and the input surface of said multi-element imagingdetector meet the Scheimpflug condition, and said telecentric lenssystem is simultaneously positioned between said sample surface and theinput surface of said multi-element imaging detector such that an imageof said sample surface produced by said multi-element imaging detectoris both substantially in focus, and such that substantially no keystoneerror is demonstrated in said image. In use said source of illuminatingelectromagnetic radiation provides illumination to a spot on a sampleplaced on said stage for supporting a sample placed thereupon.In said modified system, the reflectometer, spectrophotometer,ellipsometer or polarimeter system comprises:

-   -   a source of a sample investigating beam of electromagnetic        radiation;    -   a stage for supporting a sample placed thereupon; and    -   a detector.

In use, said reflectometer, spectrophotometer, ellipsometer orpolarimeter system is oriented to provide a sample investigating beam ofelectromagnetic radiation to said sample placed on said stage forsupporting a sample, so that it impinges on a spot thereof which issubstantially coincident with illuminating electromagnetic radiationprovided by said source of illuminating electromagnetic radiation.

It is noted that said source of illuminating electromagnetic radiationand said source of a sample investigating beam of electromagneticradiation can both be derived from a single primary source via a beamsplitter.

It is noted that addition of a polarizer between the source of a sampleinvestigating beam of electromagnetic radiation and said stage forsupporting a sample placed thereupon; and an analyzer between said stagefor supporting a sample placed thereupon and said detector,respectively, provides an ellipsometer system. And further addition of acompensator between said source of a sample investigating beam ofelectromagnetic radiation and said detector enables operation aspolarimeter.

As before, said system can further comprise a computer for receivingdata from said multi-element imaging detector and correcting it forimage aspect ratio that arises because the sample surface is approachedby the illuminating electromagnetic radiation at an inclined angle.

As before, said modified system can further comprise at least onepolarizer and/or at least compensator between said source ofilluminating electromagnetic radiation and said detector to enableeffecting a polarization state in said illuminating electromagneticradiation produced by said source thereof.

Again, as before, said modified system can provide that the telecentriclens system comprises, in sequence:

-   -   at least one lens;    -   an aperture having a diameter; and    -   at least one lens;        and said aperture diameter can be adjustable.

And, again, as room therefore exists in the present invention system,said modified system for viewing a sample at an inclined angle canfurther comprise a second imaging, or metrology, system positionedsubstantially above said sample surface and between said source of abeam of electromagnetic radiation and said detector having an inputsurface.

During use, said system for viewing a sample at an inclined angle canagain provide that illuminating electromagnetic radiation provided bysource thereof approaches the sample surface along an oblique angle,which can be at, or near the Brewster angle for the sample beinginvestigated.

A method of investigating a sample with an electromagnetic beamcomprises the steps of:

-   -   providing an imaging system for viewing a sample at an inclined        angle comprising:        -   a) a source of illuminating electromagnetic radiation;        -   b) an optional collimator;        -   c) a stage for supporting a sample placed thereupon;        -   d) a telecentric lens system; and        -   e) a multi-element imaging detector having an input surface.            Said stage and detector are oriented with respect to one            another such that the surface of said sample placed on said            stage and the input surface of said multi-element imaging            detector meet the Scheimpflug condition, and said            telecentric lens system is simultaneously positioned between            said sample surface and the input surface of said            multi-element imaging detector such that an image of said            sample surface produced by said multi-element imaging            detector is both substantially in focus, and such that            substantially no keystone error is demonstrated in said            image.            Said method then further comprises steps b), c) and d):

b) orienting said sample surface and multi-element imaging detectorsurface to meet the Scheimpflug condition and positioning saidtelecentric lens system between said sample surface and multi-elementimaging detector surface so that, in an image of said sample surfacewhen produced by said multi-element imaging detector, demonstratessubstantially no keystone error and said image is substantially in focusover its entire extent;

c) causing said source of illuminating electromagnetic radiation todirect illuminating electromagnetic radiation to optionally interactwith said collimator then proceed to reflect from said sample surface,pass through said telecentric lens system and enter said multi-elementimaging detector;

d) causing said multi-element detector to produce an image of saidsample surface that is substantially free of keystone error and issubstantially in focus.

Said method can also involve providing a reflectometer,spectrophotometer, ellipsometer or polarimeter system comprising:

-   -   a source of a sample investigating beam of electromagnetic        radiation;    -   a stage for supporting a sample placed thereupon; and    -   a detector of said sample investigating beam of electromagnetic        radiation.        When so provided, the method further provides that steps e)        and f) are further practiced, said steps e) and f) being;

e) while, or after practicing steps c) and d) to provide an image of hesample, causing said source of a sample investigating beam ofelectromagnetic radiation to direct a sample investigating beam ofelectromagnetic radiation toward said sample such that it passes throughsaid polarizer, impinges on said sample at a location substantiallycoincident with said illuminating electromagnetic radiation provided bysaid source of illuminating electromagnetic radiation, reflectstherefrom, passes through said analyzer; and

f) said detector of said sample investigating beam of electromagneticradiation receiving the sample investigating electromagnetic radiationreflected from said sample, and producing sample characterizing data.

It is to be understood that the methodology can be carried out under thecontrol of a computer and/or the methodology can include storing atleast some output provided by the detector in a non-transitory machinereadable media and analyzing at least some output provided by thedetector.

With reference to FIGS. 1A-1D, (see Detailed Description fordescription), it is further disclosed that the present inventioninvolves a camera system for monitoring a surface of a sample, infunctional combination with a reflectometer, ellipsometer, polarimeteror the like system:

wherein said reflectometer, ellipsometer, polarimeter or the like systemcomprises:

a) a source of a beam of electromagnetic radiation;

c) a stage for supporting a sample;

d) a detector;

such that in use said source of a beam of electromagnetic radiationcauses a beam of electromagnetic radiation to interact with a sampleplaced on said stage and reflect into said detector, such that samplecharacterizing data is produced thereby;

and said camera system for monitoring the surface of said samplecomprises:

e) a camera sensor plate;

f) a focusing means;

each of said camera sensor plate, focusing means and sample supportingstage each being oriented in identifiable planes, wherein:

-   -   the plane of the camera sensor plate refers to the orientation        of its surface;    -   the plane of the sample supporting stage refers to the        orientation of its surface; and    -   the plane of the focusing means is perpendicular to its optical        axis;        such that in use when said camera is positioned to observe a        sample placed on said stage for supporting a sample along a        camera viewpoint locus (VL), said camera viewpoint locus forms        an angle alpha (α) with respect to the plane of said camera        sensor plate, and proceeds from said camera sensor plate along a        substantial perpendicular to the plane of said focusing means        and along its optical axis, and such that said camera viewpoint        locus further forms an oblique angle of incidence beta (β) with        respect to a normal to a surface of said sample;

said camera sensor plate, focusing means and stage for supporting asample being oriented with respect to one another such that a projectedperpendicular to the plane of the camera sensor plate, a projected planeof the sample surface and a projected plane of the focusing meansintersect at a common point, and such that the following condition issubstantially met:Tan(α)=(X−f)/f Tan(β);where “X” is the distance from the camera sensor plate, at the point atwhich said beam passes therethrough, to a center of said focusing means,and “f” is the focal length of said focusing means and where alpha (α)and beta (β) were defined above;such that, in use the camera provides a focused view of the sample overthe area thereof viewed, while ellipsometric or the like data isacquired at small angles-of-incidence.

Further, a method of viewing a sample surface in real time duringinvestigation thereof by electromagnetic radiation, comprising the stepsof:

a) providing a system as just described; and

b) adjusting the orientations of the plane of at least one of saidcamera sensor plate, sample surface and focusing means so that theSchiempflug condition is met thereby providing an in-focus view of theentire surface of said sample while it is being investigated byelectromagnetic radiation.

Another recitation of a present invention sample imaging system formonitoring the surface of said sample during investigation thereof by areflectometer, spectrophotometer, ellipsometer or polarimeter, whilemaintaining focus and compensating for Keystone effects provides for thereflectometer, ellipsometer, polarimeter or the like system to comprise:

a) a source of a beam of electromagnetic radiation;

c) a stage for supporting a sample;

d) a detector;

such that in use said source of a beam of electromagnetic radiationcauses a beam of electromagnetic radiation to interact with a sampleplaced on said stage and reflect into said detector, such that samplecharacterizing data is produced thereby; and said sample imaging systemfor monitoring the surface of said sample comprises:

e) a camera sensor plate;

f) a focusing system.

Each of said camera sensor plate, focusing system and sample supportingstage each is oriented in identifiable planes, wherein:

-   -   the plane of the camera sensor plate refers to the orientation        of its surface;    -   the plane of the sample supporting stage refers to the        orientation of its surface; and    -   the plane of the focusing system is perpendicular to its optical        axis;        such that in use when said sample imaging is positioned to        observe a sample placed on said stage for supporting a sample        along a sample imaging viewpoint locus (VL), said sample imaging        viewpoint locus forms an angle alpha (α) with respect to the        plane of said camera sensor plate, and proceeds from said camera        sensor plate along a substantial perpendicular to the plane of        said focusing system and along its optical axis, and such that        said sample imaging system viewpoint locus further forms an        oblique angle of incidence beta (β) with respect to a normal to        a surface of said sample.

Said camera sensor plate, focusing system and stage for supporting asample being oriented with respect to one another such that a projectedperpendicular to the plane of the camera sensor plate, a projected planeof the sample surface and a projected plane of the focusing systemintersect at a common point, and such that the following condition issubstantially met:Tan(α)=(X−f)/f Tan(β);where “X” is the distance from the camera sensor plate, at the point atwhich said beam passes therethrough, to a center of said focusingsystem, and “f” is the focal length of said focusing system and wherealpha (α) and beta (β) were defined above.

In use the sample imaging system provides a focused view of the sampleover the area thereof viewed, while ellipsometric or the like data isacquired at small angles-of-incidence.

Said sample imaging system is distinguished in that the focusing systemis a selection from the group consisting of:

a) a telecentric lens system sequentially comprising:

-   -   at least one lens;    -   an aperture having a diameter; and    -   at least one lens;        and

b) two lenses which are separated by the sum of the focal lengthsthereof.

The purpose of said system is to maintain focus over a large area of asample surface and to compensate for Keystone effects.

A method of imaging a surface of a sample via a sample imaging systemfor monitoring the surface of said sample during investigation thereofby a reflectometer, spectrophotometer, ellipsometer or polarimeter,while maintaining focus and compensating for Keystone effects:

a) providing a system as just described above; and

b) adjusting the orientations of the plane of at least one of saidcamera sensor plate, sample surface and focusing system so that theSchiempflug condition is met thereby providing an in-focus view of theentire surface of said sample while it is being investigated byelectromagnetic radiation, and such that Keystone effects arecompensated.

The present invention will be better understood by reference to theDetailed Description Section, in conjunction with the Drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an exemplary sample investigation system (ES) which usesan electromagnetic beam to investigate a sample (SAM) includingconventional placement of a sample surface viewing camera (IMG).

FIG. 1B shows the “X”, “Y” and “Z” axes that apply to FIG. 1A.

FIG. 1C demonstrates relative positioning of a camera (IMG) in thesystem of FIG. 1A which removes it from a position in which itinterferes with movement of effective arms (EF) and (EF′).

FIG. 1D shows the camera (IMG) positioned as in FIG. 1C, wherein asensor plate and focusing means (FM), (eg. lens), and a sample (SAM) canbe arranged to meet a mathematical relationship defined by the“Scheimpflug” condition.

FIG. 1E shows a general system for illuminating the surface of a sample(SAM) with illuminating electromagnetic radiation (EM) provided by asource (S) thereof.

FIG. 2A shows the system of FIG. 1A, with, and additionally the presenceof a reflectometer, spectrophotometer, ellipsometer or polarimetersystem having a source (ES) of a beam of sample investigatingelectromagnetic radiation, and a detector (DET) thereof.

FIG. 2B shows that the source (S) of illuminating electromagneticradiation (EM) and the source (ES) of a beam of sample investigatingelectromagnetic radiation, can be derived from a single primary source(PS) of electromagnetic radiation, via a beam splitter (BS).

FIGS. 3 and 4 provides a schematic presentation of an imaging system(IMG), with a multi-element imaging detector (DET) and sample (SA)oriented to so that the surface of the sample (SA) and the surface ofthe multi-element imaging detector (DET) meet the Scheimpflug condition.

FIGS. 5A and 5B demonstrate the presence of, and absence of Keystoneerror.

FIG. 6 shows a sample (SAM) and a multi-element imaging detector (DET)oriented to meet the Scheimpflug condition.

FIG. 7 is included to show that the Focusing Means (FM′) in FIG. 6 cancomprise multiple lenses (L1) (L1′) (L2) (L2′) on either side of theAperture (AP).

FIG. 8 is included to show that the Focusing Means (FM′) in FIG. 6 cancomprise two Lenses (Lx) (Ly) which are separated by the sum of theirfocal lengths (F1) and (F2).

FIG. 9 is included to show that the typical configuration of theFocusing Means (FM′) sequentially comprises a Lens (L1), and Aperture(AP) and another Lens (L2),

FIG. 10 is included to show that a Compensator and/or Polarizer and/orAnalyzer can be placed between the sample (SAM) and the Imaging Detector(IMG) in FIG. 6.

FIGS. 11A, 11B and 11C are also included to show how an appropriatelyshaped Hole in an Aperture can provide a circular shaped spot on aSample (MS) resting on a Stage (STG).

FIG. 12 is included to show that a computer (CMP) can be applied tocontrol the method steps of the present invention.

DETAILED DESCRIPTION

Turning now to FIG. 1A, there is shown, in the context of an indicated“X”-“Y”-“Z” axis system, (note the “Y” axis projects into the paper, the“Z” axis projects vertically and the “X” axis projects horizontally, asindicated in FIG. 1B), an exemplary Ellipsometer System (ES) oriented inan “X”-“Y” plane, and having a Source (LS) Electromagnetic Beam (B) andDetector (DET), each of which are mounted on Effective Arms (EA), thatallow the (AOI) and (AOR) to be changed in a 2Θ manner. Also shownpresent is a Camera (IMG) removed from the Sample (SAM) along aperpendicular to its surface, (eg. along the “Z” axis), as is typicalpractice in order that the Camera (IMG) observe the Sample (SAM) surfacein focus over its field of view. For insight, also shown areEllipsometer elements including an Intensity Control Polarizer (P2), anIntensity Control Compensator (IMG), a Beam Polarizer (P), and FocusingLens (FM) all functionally attached to said Effective Arm (EF), and anAnalyzer (A) and Detector (DET) functionally attached to said EffectiveArm (EF′). However, it is to be understood that the Present Inventioncan be practiced with no more than the Source (LS) functionally attachedto Effective Arm (EF), a Sample (SAM) supporting stage, and a Detector(DET) functionally attached to Effective Arm (EF′), where only BeamIntensity change resulting from interaction with the Sample (SAM) is ofinterest.

Importantly, it should be apparent that the Effective Arm (EF) to whichthe Source (LS) of a Beam (B) of electromagnetic radiation is attached,as shown in FIG. 1A, can only rotate so far clockwise without it, or theSource (LS) bumping into the Camera (IMG), and that the Effective Arm(EF′) to which the Detector (DET) is attached can only rotate so farcounter-clockwise without it, or the Detector (DET′), bumping into theCamera (IMG). Present practice utilizing a Camera (IMG) therefore limitsachieving very small EM Beam (B) Angles-of-Incidence (AOI) andReflection (AOR). Utility would therefore be provided by positioning theCamera (IMG) otherwise than vertically above the Sample (SAM) as shownin FIG. 1A.

The present invention breaks with the FIG. 1A convention by placing theCamera (IMG) out of the way, (ie. so that the Camera (IMG) does notinterfere with the clockwise and counter-clockwise motions of therespective Effective Arms (EA) (EA′) that include the Source of an EMBeam (LS) and Detector (DET), respectively).

FIG. 1C shows the Present Invention positioning of the Camera (IMG)which can be thought of, for instance, as a location arrived at bymoving the Camera (IMG) in a −Y direction into the paper “Y”−“Z” plane,to position the Camera (IMG) as shown in FIG. 2. However, this exampleis not limiting. It is important to realize that the Camera (IMG) can beplaced essentially anywhere that allows it to have an oblique view ofthe Sample (SAM) surface being investigated by the Ellipsometer or thelike EM Beam. FIG. 1C also identifies a Camera Viewpoint Locus (VL).

FIG. 1D demonstrates the Scheimpflug condition applied to the Camera(IMG), which when met allows said Camera (IMG), when positioned, forinstance, as demonstrated in FIG. 1C, to observe the entire viewedSample (SAM) surface—in focus—, even though some portions of the Sample(SAM) are, from the Camera's viewpoint, closer thereto, and someportions of the Sample (SAM) are, from the Camera's viewpoint, furthertherefrom. FIG. 1D shows relative positioning and orientation of theCamera's viewpoint locus (VL), a Sample (SM) placed on the Ellipsometeror the like Stage (STG) for supporting a Sample, a Camera Sensor Plate(CS) and a Focusing Means (FM), (eg. lens), and indicates angels Alpha(α) and Beta (β). When the identified elements are properly orientedwith respect to one another, a mathematical relationship defined by the“Scheimpflug” condition results. In particular, Alpha (α) is the anglebetween the Viewpoint Locus (VL) and the plane of the Camera SensorPlate (CS), and Beta (β) is the oblique angle between said ViewpointLocus (VL) and a normal to the plane of the Sample (SAM). The Equationshown is the defining equation for the Scheimpflug condition:Tan(α)=(X−f)/f Tan(β);where “X” is the distance from the camera sensor plate (CS), at thepoint at which said camera viewpoint locus (VL) passes therethrough, toa center of said focusing means, and “f” is the focal length of saidfocusing means. Again, Alpha (α) is the angle between the plane of theCamera Sensor Plate (CS) and the Viewpoint Locus (VL), and Beta (β) isthe oblique angle of incidence the beam makes with a normal (NS) to theSample (SAM) surface. Note that projected planes of the Focusing Means(FM) and Sample (SAM), and a perpendicular to the Camera Sensor Plate(CS) intersect at Intersection Point (IP) when the Scheimpflug conditionis met. When the various elements are oriented as described, the Camera(IMG) will have a focused view of the viewed area of the Sample (SAM)being viewed thereby.

It is application of the Scheimpflug condition to a Camera (IMG)viewpoint locus (VL) positioned, for instance, in the “Y”-“Z” plane, asshown in FIG. 1C, to allow a view of the entire surface of Sample (SAM)in focus, while allowing the associated Ellipsometer System (ES) toachieve the smallest (AOI) and (AOR) possible for the EllipsometerSystem (ES) being applied, unaffected by Camera (IMG) presence imposedlimitations, as indicated by FIG. 1A, which is the focal point of thepresent invention.

Again, as it is important, the FIG. 1C demonstration of the positioningof the Camera (IMG) is not limiting. The Camera can be positionedessentially anywhere other than directly above the Sample (SAM) where itdoes not interfer with movement of the Effective Arms (EF) (EF′), butalso allows the Camera (IMG) an oblique view of the Sample (SAM) surfacebeing investigated by the EM Beam (B). Of course the various elements ofthe system will then require appropriate relative orientations fordifferent Camera (IMG) positioning, to satisfy the Scheimpflugcondition.

It is noted that, the FIG. 1D Camera (IMG) and Focusing Means (FM) arenot shown as encompassed within a camera housing, while not absolutelynecessary, it is common practice that they are so housed.

Continuing, there is shown in FIG. 1E a general system for illuminatingthe surface of a sample (SAM) with illuminating electromagneticradiation (EM) provided by a source (S) thereof. Note that theilluminating electromagnetic radiation (EM) reflects from said surfaceof the sample (SAM) and into a imaging system (IMG) that typically is amulti-element imaging detector. Note that a conventional location for anImaging Camera (O1) is included to distinctly show the difference inpositioning between conventional practice (Camera O1) and positioning inthe present invention practice (Imaging Means (IMG)).

FIG. 2A shows an additional view of the FIG. 1E system for illuminatinga sample surface, along with the addition of a reflectometer,spectrophotometer, ellipsometer or polarimeter system having a source(ES) of a beam of sample investigating electromagnetic radiation and adetector (DET) thereof. Also note that the Camera (O1) directly abovethe sample (SAM) is shown in dashed lines to indicate it is optional.When space is available it can be used for additional metrology orimaging even when the shown reflectometer, spectrophotometer,ellipsometer or polarimeter system is present. However, presentinvention practice does not require the Camera O1) be present. Anon-distorted view of the Sample (SAM) can be achieved using onlyImaging Device (IMG). Also shown is a COMPUTER for analysis/control.

FIG. 2B is included to show that the source (S) of illuminatingelectromagnetic radiation (EM) and the source (ES) of a beam of sampleinvestigating electromagnetic radiation, can both be derived from asingle primary source (PS) of electromagnetic radiation, via a beamsplitter (BS).

FIG. 3 provides a schematic presentation of an imaging system (IMG),with a multi-element imaging detector (DET) and sample (SAM) oriented toso that the surface of the sample (SAM) and the surface of themulti-element imaging detector (DET) meet the Scheimpflug condition. Inaddition, a Telecentric lens system (TLS) comprised of two lenses (L1)(L2) with an aperture (AP). therebetween is present between the source(S) and detector (DET). Note the sample (SAM) is shown at an angle tonormal, as is the detector (DET). This arrangement is what serves tomeet the Scheimpflug condition and provides an image of the sample (SAM)to the multi-element imaging detector (DET) that is in focus over thesurface extent of said sample (SAM). It is to be appreciated that theimaging system (IMG) of FIG. 2A corresponds to the more detailedpresentation of its components in FIG. 3. Also note that if the sample(SAM) in FIG. 3 were oriented to project in a horizontal plane, then thedetector (DET) would be projected at an oblique angle thereto, as inFIG. 2A. The imaging system (IMG) of FIG. 2A should be understood to becomprised of the sequential telecentric lens system (TLS) elements andthe detector (DET). (It is noted that telecentric lens system ischaracterized in that the entry and/or exit pupil is at infinity, where“pupil” refers to the object and/or image of an aperture).

FIG. 4 is included as it indicates that at least one optionalPolarizer/Analyzer (OPAC) can be present at a location between thesource (S) and detector (DET). Further, at least one Compensator (OPAC)could also be present at any of the shown locations. When present saidPolarizer/Analyzer or Compensator serve to impose a polarization stateon the illuminating electromagnetic radiation, which in certaincircumstances can serve to improve the image of the sample surfaceprovided by the detector (IMG).

Note that it is the meeting of the Scheimpflug condition that effectsthe in-focus image of the sample (SAM) surface at the multi-elementimaging detector (DET) surface, and it is the presence of thetelecentric lens system (TLS), or functionally equivalent that overcomeswhat is known as the “Keystone” error as demonstrated by FIGS. 5A and5B.

FIG. 5A includes distortion of a grid that constitutes the Keystoneerror. FIG. 5B shows that the telecentric lens system (TLS) eliminatesdistortion.

FIG. 6 shows a sample surface (SAM) and a multi-element imaging detector(IMG) surface oriented to meet the Scheimpflug condition which requires:Tan(α)=(X′−f)/f Tan(β);where (X′), (f), (α) and (β) are shown.

FIG. 7 is included to show that the Focusing Means (FM′) in FIG. 6 cancomprise multiple lenses (L1) (L1′) (L2) (L2′) on either side of theAperture (AP).

FIG. 8 is included to show that the Focusing Means (FM′) in FIG. 6 cancomprise two Lenses (Lx) (Ly) which are separated by the sum of theirfocal lengths (F1) and (F2).

FIG. 9 is included to show that the typical configuration of theFocusing Means (FM′) sequentially comprises a Lens (L1), and Aperture(AP) and another Lens (L2), without an Aperure (AP) present as shown inFIGS. 3 and 4.

FIG. 10 is included to show that a Compensator and/or Polarizer and/orAnalyzer can be placed between the Sample (SAM) and the Imaging Detector(IMG) in FIG. 6, much as shown in FIG. 4.

FIGS. 11A, 11B and 11C are also included to show how an appropriatelyshaped Hole in an Aperture can provide a circular shaped spot on aSample (MS) resting on a Stage (STG). Note FIG. 11A shows an Input Beamof electromagnetic radiation (LBI′) reflecting as (LBO′) from the Sample(MS). FIG. 3B shows that an Aperture with an aspect ratio other than 1.0can be placed in the Input Beam (LBI′) prior to the Sample (MS). FIG. 3Bshows that for an Angle-of-Incidence (O) of 75 Degrees, an Aspect Ratioof 4:1 is required to do so. FIG. 3C indicates that for anAngle-of-Incidence of 65 Degrees, and Aspect Ratio of 2.5:1 is required.These examples are mentioned to show that the Hole in an Aperture can beof any beneficial shape.

FIG. 12 is included to show that a computer (CMP) can be applied tocontrol the method steps of the present invention. Note, a signal (SIG)from the Detector (DET) can also be directed to said Computer (CMP), oranother computer to analyze data and provide data or analyzed dataoutput.

Having hereby disclosed the subject matter of the present invention, itshould be obvious that many modifications, substitutions, and variationsof the present invention are possible in view of the teachings. It istherefore to be understood that the invention may be practiced otherthan as specifically described, and should be limited in its breadth andscope only by the Claims.

We claim:
 1. An oblique angle imaging system, consisting of: a) a sourceof sample illuminating electromagnetic radiation; b) a stage forsupporting a sample placed thereupon, upon which is present a samplehaving a surface; c) a telecentric lens system sequentially consistingof: at least one lens; an aperture having a diameter; and at least onelens; said telecentric lens system being characterized by at least oneselection from the group consisting of:  the entry pupil issubstantially at infinity, where “pupil” refers to a selection from thegroup consisting of:  object of an aperture; and  image of an aperture;and  the exit pupil is substantially at infinity, where “pupil” refersto a selection from the group consisting of:  object of an aperture; and image of an aperture; and d) a multi-element imaging detector having aninput surface; said oblique angle imaging system source of illuminatingelectromagnetic radiation being configured to direct a beam ofelectromagnetic radiation toward said stage for supporting a sample;said multi-element imaging detector being configured to receiveelectromagnetic radiation from the surface of said sample; and saidtelecentric lens system being positioned between said sample surface andthe input surface of said multi-element imaging detector; saidmulti-element imaging detector producing an image of said sample surfacewhich is both substantially in focus, and demonstrates substantially nokeystone error.